An Independent Scientist Award would support on-going NIH-funded investigations of basic biobehavioral processes in infant rodents, especially concerning the mechanisms and function of sleep. Over the past 5 years, the PI has directed increasing resources toward one of the central questions concerning sleep: Why do infants sleep more than adults? Despite the obvious implications of this question for human health, the vast majority of sleep research continues to focus on adults. Building on recent progress in the PI's laboratory, including the development of techniques for recording neural activity in unanesthetized infant rats as they cycle between sleep and wakefulness, the current proposal has two primary aims. The first aim is to examine the sensory and neural mechanisms that underlie development of ultradian and circadian sleep- wake rhythms. A related aim is to describe the mechanisms that produce the dramatic quantitative and qualitative developmental changes in the statistical distributions of sleep and wake bouts that have now been demonstrated in rats and mice over the first three postnatal weeks. The PI is in the unique position of being able to examine the development of the neural mechanisms that generate these fundamental sleep-wake rhythms, and will do so using a variety of experimental approaches. For example, the developmental contributions of the visual system and its anatomical and functional connections with the suprachiasmatic nucleus and optic tectum will be examined. The second aim of this proposal is to employ non-traditional species to address mechanistic and functional questions concerning the development of sleep and wakefulness. For example, as a precocial species, cotton rats (Sigmodon hispidus) may help us to explain why infants born in a state of relative maturity exhibit less sleep throughout life;and as a diurnal species, Nile grass rats (Arvicanthis niloticus) may help us to identify the critical developmental changes in neural circuitry that underlie the diurnal circadian pattern of humans. The developmental framework adopted in this proposal avoids comparison of infant sleep against an adult standard but rather seeks to understand the processes of change over developmental time. One long-term goal of this project, which renewal of this award will make possible, is to further lay a foundation for our understanding of the mechanisms of sleep development so as to enable identification of the mechanisms underlying sleep dysregulation later in life.